Consumer Unit (Fuse Box)

What is the difference between an MCB and an RCBO?

An MCB protects against overload and short circuit. An RCBO does both of those AND protects against electric shock by detecting earth leakage — it's a two-in-one device.

How many circuits should my consumer unit have?

A typical 3-bedroom house needs at least 8–12 circuits. Modern homes with EVs, solar, and smart home technology may need 14–18 or more.

What is a split-load consumer unit?

A split-load consumer unit divides circuits into two groups — one group is RCD-protected, the other is not. It's an older design that's been largely replaced by full RCBO boards.

How much does a new consumer unit cost in the UK?

Typically £500–£1,000 for a standard domestic installation, including labour, the unit, and certification. Larger properties or older wiring can cost more.

Can I replace a blown fuse in my consumer unit myself?

If you have old ceramic rewirable fuses, you can replace the wire yourself legally. If you have a modern MCB, you simply reset it — but if it keeps tripping, call an electrician.

Why is my consumer unit main earth terminal loose?

A loose main earth terminal in your consumer unit is most commonly caused by a terminal screw that has worked loose over time due to thermal expansion and contraction, or was never tightened correctly at installation. This is a serious fault. Do not attempt to tighten it yourself. Turn off non-essential circuits and call a registered electrician immediately. A poor earth connection can prevent protective devices from operating correctly in a fault, creating a risk of electric shock or fire.

Why is my consumer unit making a humming noise?

A humming noise from your consumer unit is most commonly caused by a loose or vibrating busbar, a failing MCB or RCD under load, or normal low-level transformer hum from a smart meter or surge protection device. Switch off non-essential circuits and listen to isolate the source. If the hum is loud, intermittent, or accompanied by burning smell or heat, treat this as a potential fault and call a qualified electrician immediately — do not ignore it.

Why won't my consumer unit main breaker reset?

Your consumer unit main breaker won't reset because there is still a live fault on the circuit — the protective device is doing its job. The most common cause is a persistent overload, short circuit, or earth fault downstream. Before attempting to reset, switch off all individual circuit breakers first, then try the main switch. If it still won't hold, you have a fault within the consumer unit itself or the incoming supply. Do not force it. Call a qualified electrician if it refuses to latch or immediately trips again.

Why does my MCB keep tripping?

An MCB trips due to overload or a short circuit. Unplug appliances on that circuit, reset it, and plug them back one at a time to find the cause.

Why is my consumer unit making crackling noises at night?

Crackling noises from a consumer unit at night are most commonly caused by loose or corroded connections arcing under load, thermal expansion and contraction of cables and enclosures, or a failing MCB or RCD. Switch off non-essential circuits and call a Part P registered electrician promptly — arcing is a fire risk and should never be ignored. Do not attempt to open the consumer unit yourself.

Why has my consumer unit tripped out completely and won't reset?

If your consumer unit has tripped out completely and won't reset, the most likely cause is a serious earth fault, short circuit, or a faulty main switch. First, switch off all individual circuit breakers, then attempt to reset the main switch. If it still won't reset, do not force it — you have a fault that requires a qualified electrician. Avoid repeatedly forcing breakers as this can damage equipment or mask a dangerous fault. This is not a DIY repair.

What size consumer unit do I need?

Most homes need a 17th or 18th Edition consumer unit with between 8 and 16 ways (circuit breaker slots). A typical 3-bedroom house suits a 10 or 12-way unit, while larger homes or those with EV chargers, solar PV, or home offices may need 14–16 ways. Always count your existing circuits, add 20–25% spare capacity for future use, and have a Part P registered electrician size and install the unit to comply with BS 7671:2018+A2:2022.

How much does a new consumer unit cost?

A new consumer unit in the UK typically costs £300–£800 installed, including labour. A standard 10-way metal-clad unit with RCBOs costs around £400–£600 for most homes. Supply-only prices range from £50–£200 depending on the unit type. Always use a Part P registered electrician — consumer unit replacement is notifiable work under Building Regulations. Expect the job to take 4–8 hours. Get at least three quotes and ask for an Electrical Installation Certificate upon completion.

Can I replace a fuse board myself?

No — replacing a fuse board (consumer unit) yourself is not legal in England, Wales, or Scotland unless you are a Part P registered electrician or work under a building notice. The work is notifiable under Part P of the Building Regulations. An unregistered person must submit a building notice to their local authority before starting work. Using a registered electrician ensures the installation is certified, tested to BS 7671 18th Edition, and safe for your household.

Why is my breaker crackling?

A crackling breaker is most commonly caused by a loose or corroded connection at the breaker terminal, creating arcing. Switch off the affected circuit immediately and do not ignore it — arcing inside a consumer unit is a fire hazard. A Part P registered electrician should inspect and re-terminate the connection before the circuit is used again. Less commonly, the breaker itself may be faulty or failing internally. Never attempt to open or work inside your consumer unit yourself.

Why does my breaker keep tripping?

Your breaker keeps tripping because a circuit is overloaded, there's a fault (short circuit or earth fault), or the breaker itself has failed. The most common cause is overloading — too many appliances on one circuit. Start by unplugging devices on that circuit and resetting. If it trips immediately with nothing connected, stop and call a qualified electrician. Never tape or bypass a tripping breaker — it exists to protect you and your home.

Why is my consumer unit hot?

A warm consumer unit is normal under load, but a hot one usually means loose connections, overloaded circuits, or a faulty breaker. Touch the front cover — if it's uncomfortably hot or you smell burning, switch off the main isolator immediately and call a Part P registered electrician. Never open the consumer unit yourself. Mild warmth during peak usage is acceptable; sustained heat or a burning smell is a serious fire risk requiring urgent professional attention.

Why is my fuse board buzzing?

A buzzing fuse board is most commonly caused by a loose connection, an overloaded circuit, or a faulty MCB or RCD. In some cases, normal low-level transformer hum from an RCD or RCBO is harmless, but a loud or persistent buzz should never be ignored. Switch off non-essential circuits and call a Part P registered electrician to inspect the board. Do not attempt to open the consumer unit yourself — live busbars inside can cause fatal electric shock.

Why is there a strong burning smell coming from my consumer unit only at night?

A burning smell from your consumer unit at night is most likely caused by a loose or overloaded connection that heats up under sustained evening load — things like storage heaters, overnight appliances, or EV chargers drawing current for hours. This is a serious fire risk. Do not ignore it. Turn off the main switch at your consumer unit if the smell is strong, and call a qualified electrician as an emergency. Never assume a burning smell from electrical equipment will resolve on its own.

Why is my old fuse box making popping sounds?

Popping sounds from an old fuse box are most commonly caused by arcing inside loose or corroded connections, a failing rewirable fuse, or an overloaded circuit. Switch off the main switch immediately and do not use the fuse box until a qualified electrician has inspected it. Arcing inside a consumer unit is a serious fire risk. Old fuse boards without RCD protection offer no arc fault protection, making a full consumer unit replacement the safest long-term solution.

Why is there water inside my consumer unit?

Water inside a consumer unit is most commonly caused by condensation from a cold incoming metal tails pipe sweating inside the enclosure, or by a leak from above tracking down cables. This is a serious electrical safety hazard — do not touch the unit. Switch off the main incomer if safe to do so, leave all circuit breakers alone, and call a registered electrician immediately. Water and live electrical equipment can cause electrocution, fire, or nuisance RCD tripping. Never attempt to dry it yourself.

When does my consumer unit need upgrading?

Your consumer unit needs upgrading if it's more than 25–30 years old, has no RCD protection, uses old rewirable fuses, or has failed an EICR inspection.

Do I need to upgrade my fuse box?

If you have old rewireable fuses, no RCD protection, or a plastic consumer unit fitted before 2016, upgrading is strongly recommended.